There are various printing systems, in general, such as relief printing (flexographic printing, letter press or the like)/gravure printing (intaglio)/offset printing (lithographic plate). Among them, the relief printing method is an easy printing system, can print information on various printing media at low cost, can also easily print information at a high speed, and accordingly has been weighted heavily among recent printing methods. In addition, in recent years, the flexographic printing, which is used particularly for a packaging material such as a corrugated cardboard, a paper container, a paper bag and a soft film for packaging, an architectural material such as a wall paper and a decorative laminate, label printing and the like, has higher definition and higher versatility among various relief printing methods, and has received attention. A general relief printing plate is produced through an exposing step, a developing step and a post-treatment step, and often employs a photosensitive resin as is described in Patent Documents 1 to 3, for instance. The relief printing method also includes a method for directly forming a relief image on an original printing plate with a laser beam, which does not need the developing step. The material to be used for the above method includes a plate made by heating/vulcanizing a synthetic rubber such as EPDM and a silicone, and a plate obtained by photo-curing a photosensitive resin by light exposure, as is described in Patent Document 4.
The photosensitive resin plate can be applied to various applications not only for the relief printing plate but also for forming a pattern with the use of a designed roll by surface finish such as embossing finish, forming a profiling pattern, for forming patterns of a conductor/a semiconductor/an insulator, in an electric component, for forming a pattern of a functional material such as an anti-reflection film, a color filter and a (near) infrared cut filter, in an optical component, further for forming coatings/patterns of an oriented film, an underlayer, a light-emitting layer, an electron transport layer and a sealing layer, in the production of a display device such as a liquid crystal display and an organic electro luminescence display, for a blanket for ink transfer, which does not have a pattern formed thereon, or for a roll for adjusting the quantity of an ink while contacting an anilox roll.
For instance, a printing method with the use of a flexographic printing plate is a method in which ink is supplied onto the surface of the projecting part in a printing plate having recessed and projected portions by using an ink supply roll or the like, and subsequently the printing plate is brought into contact with a substrate to transfer the ink on the surface of the projecting part onto the substrate. In such a flexographic printing method, the ink often attaches to a shoulder part of the projecting part of the printing plate in a long printing period of time, or the ink enters the recessed parts of the printing plate (hereinafter referred to as “plate surface blemish”). As a result, there is a case where even a portion which is not contained in an original design is printed. In such a case, it is necessary to stop printing once, and to wipe off the unnecessary ink of an image of the printing plate with a cloth or the like by using a cleaning liquid such as alcohol, which becomes economically disadvantageous.
Particularly in recent years, the relief printing method has a trend of being applied to high-definition printing, and the printed matter is required to show no irregularity of dots, the uniformity of widths of a character, a thin line or a reverse line, and the uniformity of the concentration of a solid part. When the ununiform irregularity and the blemish are formed on the surface of the plate, the irregularity can be transferred onto the printed matter.
Similar problems occur also when a pattern is formed with the use of a photosensitive resin plate. The deterioration of the uniformity of the pattern and the pattern blemish due to the plate surface blemish may lead to the aggravation of the releasability of a body to be contacted or a mold, particularly when a surface-finished pattern by embossing finish or the like and a profiling pattern are formed.
Various methods are proposed for preventing the plate surface blemish of a printing plate. Patent Document 5 discloses a technology of making an organofluoric compound attach to the surface of the plate with a brush coating method or a spray coating method.
Patent Document 6 discloses a method in which a material selected from among a silane coupling agent, silicone oil and silicone grease is added to the inner part of a photosensitive resin, and then the material is made migrate to the surface of the photosensitive resin.
Patent Document 7 proposes a method in which a mixture of a water-based emulsion of a silicon-based compound or a fluorine-based compound and an aqueous resin is applied to the surface of the plate.
Patent Document 8 proposes a method in which a hydrophobic compound which is copolymerizable with a polymerizable material in a water-developable composition and contains fluorine, chlorine and silicon is added to the inner part of the composition, and the contact angle of the surface of the plate is increased.
Patent Document 9 proposes a method for producing a photosensitive resin plate, which includes making a solution containing a silicon-based compound and/or a fluorine-based compound attach to a plate surface prior to the post-exposure step, in order to prevent the plate surface blemish for a long period of time.
Patent Document 10 proposes a method in which a water-developing photosensitive resin plate for relief printing is brought into contact with a liquid containing a modified silicone compound or a modified fluorine compound, after an exposure step in a plate making process.
Patent Document 11 proposes a method for producing a laser-engraved printing plate, which includes a step of immersion in a treatment liquid containing an organosilicon compound having a number average molecular weight of 100 or more but 100,000 or less, or a step of post-exposure to a laser beam having a wavelength of 200 nm or more but 450 nm or less after application of the treatment liquid.
Furthermore, a technology is also known which makes a paraffin wax (waxy hydrocarbon) contained in a resin composition and bleed onto the surface of the printing plate, as is described in Patent Document 12.
Patent Document 1: Japanese Patent Laid-Open Publication No. 10-171111
Patent Document 2: Japanese Patent Laid-Open No. 63-088555
Patent Document 3: Japanese Patent Laid-Open No. 05-134410
Patent Document 4: Leaflet of WO 03/022594
Patent Document 5: Japanese Patent Laid-Open No. 51-40206
Patent Document 6: Japanese Patent Laid-Open No. 60-191238
Patent Document 7: Japanese Patent Laid-Open No. 2002-292985
Patent Document 8: Japanese Patent Laid-Open No. 06-186740
Patent Document 9: Japanese Patent Laid-Open No. 2005-84418
Patent Document 10: Leaflet of WO 05/064413
Patent Document 11: Japanese Patent Laid-Open No. 2005-212144
Patent Document 12: Japanese Patent Laid-Open No. 62-95310